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How to control the speed of a 24vdc pump from circulating water temperature?

Alec_t

Jul 7, 2015
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What is the pot resistance, end to end?
As for mounting the probe, you could embed it in epoxy putty conformed to the pipe shape to make good thermal contact.
 

cygnusv

Oct 7, 2014
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Hi Alec_t

How would I measure that? I'm a bit of a newbie to all this but hoping to learn. I've got a decent multimeter...

Fascinating things these forums. These messages are doing a round trip of 25,000 miles, yet you're only about 200 miles away! Excellent!!
 

Alec_t

Jul 7, 2015
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How would I measure that?
With a bit of luck you'll see the value stamped or printed on the pot. If not, you could try using the Ohms range of your meter to measure (with no power on the circuit) the resistance between the two outer pins of the pot and, for confirmation, from the centre pin to each outer pin in turn. This isn't foolproof, since the pot has other things connected to it which will probably affect the measurements. It helps sometimes to make one measurement then reverse the probes and make a second measurement of the same component. If the two measurements don't tally then they are suspect and indicate some other component is affecting the result.
 

CDRIVE

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Just unplug the Pot from the board before you measure it. This way it's divorced from the board. ;)

Chris
 

cygnusv

Oct 7, 2014
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Hi Alec_t and Chris
The pins are as follows

GND (RED)
0-5 (WHITE)
5V (BLACK)

I've measured my values using the 20K scale on the meter

GND TO BLACK = 9.71 with the knob turned to both min and max

0.5 TO GND = 9.7 with knob fully c/w and 0 when adjusted fully anticlockwise
0-5 -TO 5V = 0 when fully on (c/w) and 9.7 when fully off

I'd actually checked these values befor I saw Chris's message, but because the values match I haven't done the measurements again disconnected.

The meter took its time to reach the above values and would probably have risen a bit higher - maybe meant to be 10K Ohms I guess.

This help?

Stu
 

CDRIVE

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Yes, that's a 10KΩ Pot.

Chris
 

cygnusv

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Yes, that's a 10KΩ Pot.

Chris

So I'd be looking for a 10KΩ thermistor? Would I need anything else to make it work?

Sadly the sensor and the PWM are about 2 metres apart - is this an issue?

Stu
 

Alec_t

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A 10k thermistor should be ok. You could probably use it in series with the existing pot. Here are two options, one of which should put the trigger point in the right ball park :
Varistor+pot.PNG
 

cygnusv

Oct 7, 2014
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A 10k thermistor should be ok. You could probably use it in series with the existing pot. Here are two options, one of which should put the trigger point in the right ball park :
View attachment 27606

What would be the advantage of this over simply replacing the pot with the thermistor? I know I'm showing my ignorance but I am curious and more than willing to learn.

Stu
 

CDRIVE

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Not to be anal but a Varistor is not a Thermistor but I'm sure Alec knows that and it's simply a typo. That said you can't replace the pot with only a Thermistor. It will have to be wired as Alec shows it in option 2 or 3. The Pot (wired as a Rheostat) is needed to create a calibrated voltage divider that mimics the Pot action in Option 1.

Chris

Edit: No, I don't think 2 meters is going to be an issue but using shielded cable would be advantageous.
 

cygnusv

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High CDRIVE

Many thanks. I've ordered the thermistor but that won't arrive for a couple of weeks. I understand now the reason for wiring this way. Would you suggest soldering the wires together to make these connections or going through some kind of joint?
The cables on the ordered part may not be shielded. Is there a suitable enclosure I can use?

Stu
 

CDRIVE

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High CDRIVE

Many thanks. I've ordered the thermistor but that won't arrive for a couple of weeks. I understand now the reason for wiring this way. Would you suggest soldering the wires together to make these connections or going through some kind of joint?
The cables on the ordered part may not be shielded. Is there a suitable enclosure I can use?

Stu
The only component that will be connected to the pipe end of the cable will be the Thermistor. The Pot remains with the PCB.

Is the end of the Pot's shaft slotted?

Post the link to Thermistor you purchased.

Ebay has plenty of plastic and aluminum enclosures. On that note the supplier of your PWM board may stock them too.

Chris
 

cygnusv

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The only component that will be connected to the pipe end of the cable will be the Thermistor. The Pot remains with the PCB.

Is the end of the Pot's shaft slotted?

Post the link to Thermistor you purchased.

Ebay has plenty of plastic and aluminum enclosures. On that note the supplier of your PWM board may stock them too.

Chris

Hi Chris

http://www.ebay.co.uk/itm/201525661...49&var=500712525652&ssPageName=STRK:MEBIDX:IT

The base of the pot is solid with a knob on the other end. Connected to the board remotely with 3 wires

Thermistor link above

My badly worded question was for shielding the wires from the thermistor, though I will require an enclosure for the PWM when I fit it

My basic question was about how to make the series connection between the PCB and the thermistor. Solder the thermistor wires to the wires that connect the pot with the board or use some sort of electrical chocolate type connector?

Stu
 

Alec_t

Jul 7, 2015
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My badly worded question was for shielding the wires from the thermistor
You may get away without shielding if you connect a capacitor (try 100nF) across the thermistor terminals at the pcb end to shunt away any noise pickup. The circuit should be responding only to slowly varying input.
Soldering the cable end connections is probably best IMO, but the cable also needs physically anchoring so that vibration doesn't fracture the joint/wire in time. Hot melt glue or a cable tie could be used for the anchoring.
 

CDRIVE

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You have to remove the knob to see if the Pot shaft is slotted on its end. I ask because the Pot setting is something that should not be easily changed by accidentally bumping it. So it's best to not leave the knob on it.

Here's a modified schematic of my last one showing the remote Thermistor and a noise bypass cap (100nF) connected to the input of the PWM board.

Yes, soldering would be your best choice of hookup. If you use a metal enclosure all wires entering and exiting the enclosure should be fed through grommets. Not a concern if it's plastic but some sort of strain reliefs should be employed.

Chris

upload_2016-6-30_11-53-22.png
 

CDRIVE

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Stu, this is a rough idea of how you can put this all together. Please keep in mind that I'm an avid cyclist that likes to do 30 miles daily (minimum),.. rain or shine, hot or cold. Recently my right 70 year old knee has been rebelling and cutting back my mileage. Consequently I socked down nearly a quart of Chardonnay while drawing this. If anyone sees any glaring errors don't hesitate to call me on it.

Chris

upload_2016-6-30_23-29-2.png
 
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CDRIVE

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Here's another pictorial to help make the wiring clear.
(1)The Black & White wires from the plug to the Pot remain intact.
(2) Solder the Cap to the Pot's terminals.
(3) Solder one of the Thermistor cable wires to the Pot's terminal as shown.
(4) Cut the Red wire from the Pot's plug and connect it to the other Thermistor lead.
(5) Solder the end of the Red wire still connected to the Pot to the center pin (wiper) of the Pot.

Chris
upload_2016-7-1_0-47-55.png
 
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cygnusv

Oct 7, 2014
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Collectively these last few replies have completely cleared up what I need to do. Many thanks.
We're completely refurbing the cabin where the control gear and pump will be so I'll report on progress and results in a week or two.
Sorry about the knee Chris - but the Chardonnay sounds like an excellent idea!
Thanks again everyone
 

CDRIVE

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You're welcome Stu. Here's some important notes that should receive serious consideration.

(1) The circuit as it's currently drawn has the ability to adjust the control (input) voltage to 0V when the Pot is turned to its fully clockwise extreme.

(2) The circuit I drew assumed that an increase in control (input) voltage produces a longer PWM on time, thus increasing motor speed.

(3) Keeping notes 1 & 2 in mind I drew my pictorials where turning the Pot clockwise will reduce motor RPM because this would be the intuitive direction to increase water temperature.

Earlier in this thread I stated that I have no idea if increasing the control voltage translated into increasing PWM (On Time) that will translate to increasing RPM. That was the post that I commented on deciphering Chinese tech data.

I just went back to the Ebay link and looked at the photo that includes the Pot plugged into the board. Keeping in mind that turning the Pot clockwise to increase RPM is intuitive (except for women:D) my circuit's analog logic may be backward. This is because we never did determine if an increase in control voltage translates to increase in RPM. Looking at that Photo tells me the opposite is true.

So what's the bottom line?

As with all prototyping design nothing should be considered final and permanent unit all experimentation is completed and you're satisfied with the results. This means all connections should be only tacked soldered until final design. Live circuit tests should be done prior to stuffing everything in an enclosure.

I would suggest that you experiment with a with a 12V or 24V incandescent lamp (torch) as a load with the Pot wiring unmodified. Then measure the control voltage between GND (Black) and Pot's wiper (White) while turning the Pot clockwise and counter clockwise while also observing the brilliance of the lamp.

On a final note I would not recommend using your boat's storage cells as a supply for prototyping. They're WAAAAAY to powerful and totally unforgiving if you have an "Oh Sh!T!" moment. A 12VDC wallwart plugged into shore power would be sufficient for experimental prototyping. Even a little 9V battery and low current lamp load would suffice for testing. I guess an LED with a 330Ω series resistor should work for a load too but incandescent lamps respond to PWM better and are more easily seen by the human eye.

Lets us know when you start your experiments.

Alec, take a look at this photo. Assuming clockwise rotation increases pulse width do you agree that this looks like decreasing control voltage increases pulse width?

Chris
$_57.JPG
 
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